Apparatuses for controlling the temperature of a liquid are currently used in various technical fields. For instance, in biochemistry, temperature controlling units for controlling the temperature of a sample liquid are used. Examples of known temperature controlling units include a PCR machine for performing a PCR (polymerase chain reaction) method. As to PCR methods, description is given in e.g. Patent Documents 1 and 2 identified below.
FIG. 17 shows an example of conventional PCR machine. The illustrated PCR machine X2 includes a holding block 91, a heating block 92 and a cooling block 93. In the PCR machine X2, a cycle including thermal denaturation, annealing and elongation is repeated a plurality of times.
The holding block 91 is formed with a plurality of recesses 91a for receiving tubes 94. Each of the tubes 94 contains a reaction sample liquid or the like for performing a PCR method. The reaction sample liquid contains template DNA, primer DNA, DNA polymerase, and dNTP. The holding block 91 is transferred by a transfer member (not shown) to a position above the heating block 92 (FIG. 18) or a position above the cooling block 93 (FIG. 19). The heating block 92 is provided for supplying heat to the holding block 91 and thermally connected to a heating device (not shown). The cooling block 93 is provided for taking heat from the holding block 91 and thermally connected to a heat-absorbing device (not shown).
In the PCR machine X2, a PCR method is performed as described below, for example.
First, the holding block 91 is placed on the heating block 92 and heated by the heating block 92 (temperature increase step). In this step, the heating block 92 is kept at a thermal denaturation temperature T11 (e.g. 95° C.) by the heating device.
When the holding block 91 substantially reaches the thermal denaturation temperature T11, the reaction sample liquid in the tubes 94 held by the holding block 91 also reaches the denaturation temperature T11, so that a thermal denaturation step starts. In the thermal denaturation step, two strands of a template DNA are separated from each other.
After the thermal denaturation step, the holding block 91 is transferred to and placed on the cooling block 93 and cooled by the cooing block 93 (temperature reduction step). In this step, the cooling block 93 is kept at an annealing/elongation temperature T12 (e.g. 60° C.) by the operation of the heat-absorbing device, not shown.
When the holding block 91 substantially reaches the annealing/elongation temperature T12, the reaction sample liquid in the tubes 94 held by the holding block 91 also reaches the annealing/elongation temperature T12, so that an annealing/elongation step (the step in which annealing and elongation proceed at the same time) starts. In the annealing step, each single-stranded DNA of the template combines with a primer (containing a base sequence complementary to part of the single-stranded DNA). In the elongation step, at the 3′ end of the primer combined with the single-stranded DNA of the template, a DNA strand containing a base sequence complementary to a single-stranded DNA is elongated or synthesized.
In the PCR machine X2, the cycle including the above-described steps is repeated a plurality of times, whereby apiece of DNA having a predetermined base sequence is amplified.
Patent Document 1: JP-A-4-501530
Patent Document 2: JP-A-6-277036
FIG. 20 is a graph showing an example of temperature change of a reaction sample liquid in each cycle of the above-described PCR method performed by the PCR machine X2. As shown in the graph of FIG. 20, in the temperature increase step, the temperature increase speed in a temperature range close to the target temperature (thermal denaturation temperature T11) is considerably low as compared with the temperature increase speed in the initial stage of the temperature increase step. In this way, with the PCR machine X2, the reaction sample liquid reaches the thermal denaturation temperature T11 after going through the temperature range in which the temperature increase speed is considerably low. Thus, it is necessary to secure sufficient time for the temperature increase step. Moreover, in the temperature reduction step, the temperature reduction speed in a temperature range close to the target temperature (the annealing/elongation temperature T12) is considerably low as compared with the temperature reduction speed in the initial stage of the temperature reduction step. In this way, with the PCR machine X2, the reaction sample liquid reaches the annealing/elongation temperature T12 after going through the temperature range in which the temperature reduction speed is considerably low. Thus, it is necessary to secure sufficient time for the temperature reduction step as well. Thus, the PCR machine X2 is not suitable for completing the temperature increase step and the temperature reduction step in a short period of time. In other words, the PCR machine X2 is not suitable for quickly changing the temperature of a reaction sample liquid (liquid).